Printed circuit boards (PCBs) are substrates often used to mount electronic components housed within integrated circuit (IC) packages. For example, a semiconductor die is often mounted on a PCB and then covered with an overmold in order to protect the semiconductor die. Traditional PCBs often have a substrate body formed from a laminate. The substrate body is typically formed from a stack of substrate layers formed from a laminate. To connect the input and output structures of the semiconductor die to other electronic components within the IC package and/or to input and output structures of the IC package accessible externally from the IC package, a conductive structure is often integrated into the substrate body. The conductive structure typically has metallic layers formed horizontally between the substrate layers and/or on a substrate surface. These metallic layers are shaped to form conducting structures, such as traces, terminals, connections pads, and the like to connect electronic components within the IC package and/or the input and output structures of the IC package to the electronic components.
A vertical interconnect access structure (via) is often provided in the conductive structure to extend vertically and through a substrate layer. One of the problems with traditional laminate technology used to form a via is that the via can often be partially misaligned, thereby resulting in unintentional connections, noise, and shorts. To ameliorate this problem, the conductive structure being connected by the via may be formed so as to have a larger footprint than the via, thereby preventing unintentional connections and shorts due to misalignments.
FIG. 1 illustrates one embodiment of a PCB 10 having a substrate body 12 and a conductive structure 14 integrated into the substrate body 12. The substrate body 12 is made from a laminate. The substrate body 12 is formed from a stack of substrate layers 16. The conductive structure 14 is formed from conductive layers 18 and conductive vias 20 that extend through the substrate layers 16 to provide connections between the conductive layers 18. Note that the conductive vias 20 shown in FIG. 1 are formed simply as a conductive post.
As shown in FIG. 1, the conductive structure 14 is shaped to provide a three dimensional (3D) inductor 22, which in this embodiment is a solenoid inductor. Each of the conductive layers 18 is shaped to form a winding 24, and the conductive vias 20 connect the ends of the windings 24 on different conductive layers 18. Note however that the footprint of the ends of the windings 24 are larger than the footprint of the attachment surface of the conductive vias 20, and thus an outer contour of the ends extends horizontally past the attachment surface of the conductive vias 20. This was done to prevent via misalignments and undesired shorts when the 3D inductor 22 was being formed. However, one of the problems with this arrangement is that current will be misdirected to flow horizontally through the outer contour of the ends that extends horizontally past the attachment surface of the conductive vias 20. This unfortunately results in stray magnetic behavior and causes the current to have to travel farther. As such, this results in a degradation of the quality (Q) factor of the 3D inductor 22. Another problem with the arrangement shown in FIG. 1 is that there is a large difference between the thickness of the conductive layers 18 and the depth of the conductive vias 20. This also degrades the Q factor of the 3D inductor 22 and places hard limitations on the routing density of the conductive structure 14.
FIG. 2 illustrates one embodiment of a 3D inductor 26 created in a PCB 28. The PCB 28 has a substrate body 30 and a conductive structure 32 that is integrated into the substrate body 30. The 3D inductor 26 is formed as part of the conductive structure 32 on and within the substrate body 30. The 3D inductor 26 shown in FIG. 2 is described in further detail in U.S. Pat. No. 9,196,406 entitled “HIGH Q FACTOR INDUCTOR STRUCTURE” issued on Nov. 24, 2015, which is hereby incorporated by reference in its entirety.
The 3D inductor 26 provides a conductive path 34 that extends in all three dimensions but curves back in on itself. The conductive path 34 therefore surrounds a perimeter of a 3D area and encloses a 3D volume 36. To form the conductive path 34, the 3D inductor 26 comprises four elongated via columns (referred to generically as element 38, and specifically as elongated via columns 38a, 38b, 38c, and 38d). Each of the elongated via columns 38 is formed by a stack of elongated vias 40 (not all labeled for the sake of clarity). Also, to form the conductive path 34, the 3D inductor 26 of FIG. 2 also comprises three connector plates 42, 44a, and 44b. The connector plate 42 connects the elongated via column 38b to the elongated via column 38c on a first vertical side SA of the 3D inductor 26. On a second vertical side SB of the 3D inductor 26 that is antipodal to the first vertical side SA, the connector plate 44a connects the elongated via column 38a to the elongated via column 38b, and the connector plate 44b connects the elongated via column 38c to the elongated via column 38d. The 3D inductor 26 of FIG. 2 further comprises two terminal plates 46 and 48 to form part of the conductive path 34. The terminal plates 46 and 48 comprise a terminal connection for the 3D inductor 26 and are connected to the elongated via columns 38a, 38d, respectively, at the first vertical side SA.
Current flows across the terminal plate 46 down the elongated via column 38a to the connector plate 44a. The current flow continues across the connector plate 44a up through the elongated via column 38b to the connector plate 42. The current flow then continues across the connector plate 42 down through the elongated via column 38c to the connector plate 44b. The current flow continues up through the elongated via column 38d to the terminal plate 48.
From the above current flow description, it can be seen that the 3D inductor 26 provides a significant amount of magnetic field cancellation since the majority of sections along the conductive path 34 can be matched to a symmetrical section where current flows in the opposite direction. This allows the 3D inductor 26 to be utilized to provide weak magnetic coupling between resonators and thereby to provide filtering circuit with a high quality (Q) factor.
As shown in FIG. 2, each of the elongated vias 40 in columns 38 includes a conductive post 50 (not all labelled for the sake of clarity). Additionally, except for the elongated vias 40 connected to the connector plate 42 and the terminal plates 46, 48, each of the elongated vias 40 has a capture pad 52 (not all labelled for the sake of clarity). Each of the conductive posts 50 extends vertically through a one of the substrate layers 54 of the substrate body 30. The capture pads 52 are formed by conductive layers 56 (not all labeled for the sake of clarity) within the substrate body 30. The capture pads 52 allow for the conductive posts 50 of the next elongated via 40 in the columns 38 to be formed while avoiding undesired connections resulting from misalignments. However, the capture pads 52 have a much larger footprint than the conductive posts 50. Since the high frequency RF current travels along the metal surface, the current will travel horizontally along the surface of the capture pads 52 as the current propagates through the column 38. Accordingly, the current has to travel a greater distance as the current propagates through the columns 38. Furthermore, the capture pads 52 result in significant Q factor degradation due to magnetic field distortions resulting from the current propagating horizontally through the capture pads 52.
Accordingly, better techniques are needed in order to connect conductive structures within a 3D inductor using vias while still preventing undesired connections from via misalignment.